A gas turbine engine generally comprises a compressor section, a combustion section and a turbine section. The combustion section includes a plurality of combustors arrayed about the combustion section that are in fluid communication with a combustion section interior. The compressor section includes a series of stages, each stage including a row of stationary stator vanes and a row of rotating blades, used to compress air in order to provide a compressed air flow to the combustion section. In the combustion section, the air is mixed with a fuel, such as natural gas, and ignited to create a hot working gas. The turbine section includes a plurality of turbine blades arranged in a plurality of rows. The hot gas expands through the turbine section where it is directed across rows of blade assemblies by associated stationary vanes. The blade assemblies are attached to a rotatable shaft. As the hot gas passes through the turbine section, the gas causes the blades and thus the shaft to rotate, thereby providing mechanical work.
An exemplary compressor section 10 is shown in FIG. 1. The compressor section 10 may be housed within a turbine outer casing or shell 12. The outer casing 12 may include two generally semi-cylindrical halves that are secured together. The outer casing 12 encloses, among other things, a rotor having a plurality of disks 14 that extend radially outward therefrom. A plurality of airfoils or blades 16 is mounted on each disk 14 to form a row. The rows of blades 16 alternate with rows of stationary airfoils or vanes 18. In some instances, the vanes 18 may be provided in the form of a diaphragm 20. Each diaphragm 20 may include inner 22 and outer 24 radial bands or shrouds, with a plurality of vanes 18 circumferentially arrayed therebetween. The diaphragm 20 may also be made of two substantially semi-circular halves similar to the outer casing 12. In addition, the outer casing 12 may include a circumferential slot or outer hook 26 along its inner peripheral surface 27 for receiving projecting elements 32 of the outer shroud 24 so as to attach the diaphragm 20 to the outer casing 12.
Referring to FIG. 2 in conjunction with FIG. 1, a seal holder 28 may be attached to the inner shroud 22 of the diaphragm 20. One or more seals 30 may extend from the seal holder 28. One or more surfaces of a seal holder 28, such as an upstream face 34, is spaced apart from a downstream face 36 of an adjacent disk 14 by a gap 38. During operation, at least one area or region of the outer hook 26 becomes worn (i.e. either upstream 40 or downstream 42 wear regions or both). This causes the seal holder 28 to move upstream due to the pressure difference between leading 44 and trailing 46 edges of an associated vane 18. As a result, an upstream gap 38 between the vane 18 and an upstream disk 14 reduces over time as wear occurs which may ultimately result in undesirable contact 48 (see FIG. 3) between the seal holder 28 and the 14 disk and thus possible damage to the disk 14, the seal holder 28 and/or the compressor section 10.
In order to avoid such damage, the hook wear regions 40, 42 and associated interfaces/components are visually inspected in order to assess the level of wear that has occurred during gas turbine operation. The inspection occurs at periodic intervals at which time the gas turbine is shut down. Visual inspection of hook wear requires removing a turbine cover (i.e. performing a cover lift) or disassembly of other portions of the gas turbine to provide access to the hook wear regions 40, 42 and associated components. Typically, an inspection/service team visually inspects the outer hook 26 to determine a level of functionality of the outer hook 26 (level of wear, whether there are any cracks, assessment of coating quality etc. if any) and provide an estimate of the remaining life of the outer hook 26 and other components. Depending on the level of wear, parts or components may need to replaced or repaired. However, such visual inspections are labor intensive, time consuming and expensive and typically occur during a scheduled maintenance after a predetermined time period or during a major site outage. Thus, information regarding component wear rates during other time periods, for example, initial wear rates early in an operating schedule, are not available.